1. Field of the Invention
The present invention relates to a blow molding device adapted to form a blow molded article having a built-in part composed of a thermoplastic synthetic resin in an interior space thereof, and a blow molding method.
2. Description of Related Art
Conventionally, tubular blow molded articles, such as fuel tanks for use in automobiles, etc., have been formed of metal, but, in recent years, thermoplastic synthetic resins have been frequently used to form such tubular blow molded articles, because they can effect lightweight automobile bodies, no rust is generated therein, and they can be readily formed into desired configurations.
In many cases, the tubular articles made of thermoplastic synthetic resins have been formed by blow molding, because tubular bodies can be readily formed therewith. Upon blow molding, a parison of a molten thermoplastic synthetic resin is extruded downwardly into a cylindrical configuration, and air is blown into the parison with the parison held with a blow mold, thereby forming the tubular bodies.
On the other hand, upon blow molding, built-in parts such as valves, baffle plates adapted to restrain noise caused by the flowing of fuel, etc. may be required to be provided in interior spaces of the blow molded articles, such as fuel tanks.
In order to provide the built-in parts in the interior spaces of the blow molded articles, a molding device shown in FIG. 1 has been used (see published Japanese patent applications No. Hei 9-174670 and Hei 8-72129, for example.). A built-in part 10 is held in a cavity of a blow mold 12 with a holding rod 14, and a parison 16 is lowered. Then, the blow mold 12 is closed with the built-in part 10 held with slide cores 18, and the parison 16 is pinched with pinching plates 20 to form the blow molded article.
When the dimensions of a built-in part increase, as shown in FIG. 2, a built-in part 22 held with a holding rod 24 is inserted in an interior space of a parison 26, and the built-in part 22 is held between slide cores 28 of a blow mold 30. But, upon inserting of the built-in part 22, it is necessary to prevent the built-in part 22 from contacting an inner wall of the parison 26.
To this effect, the diameter of the parison 26 must be increased. But, when the diameter of the parison 26 increases, the parison 26 is extruded exceeding a required amount for forming the blow molded article, and as a result, the amount of flash around the resulted blow molded article increases to cause a waste of material. In addition, die cores adapted to extrude the parison 26 become large, and a large number of die cores are required.
In order to solve the above-described problem, as shown in FIG. 3, a lower end of a parison 32 extruded from a die core 34 is enlarged with a parison expander 36 below a blow mold 38, and the lower end of the parison 32 is held with a tip end of a built-in part holding unit 40 and a parison holding unit 42. A built-in part 44 is held within an airtight guide tube 46 of the built-in part holding unit 40, and is held with a lower guide plate 48 in an airtight condition.
In this case, as shown in FIG. 4, in the pre-blowing process, the parison 32 is expanded in an airtight condition while holding the parison 32 with the tip end of the built-in part holding unit 40, and by sliding a built-in part holding rod 50, the built-in part 44 can be inserted into the parison 32. Then, the built-in part 44 is held with slide cores 52
However, as shown in FIG. 3, in order to position the built-in part holding unit 40 holding the built-in part 44 below the blow mold 38, and slide the built-in part holding rod 50 upwardly and downwardly, a pit 54 adapted to accommodate the built-in part holding rod 50 having a long shaft must be provided below the blow mold 38 so that a sufficient space is required and accordingly the production costs increase.